1. Field of the Invention
The present invention relates to a simultaneous both-sided ironing-deep drawing process, and in particular to an ironing-deep drawing process for controlling the longitudinal residual stress in the wall of ironed-deep drawn articles.
2. Description of the Related Art
In general, the ironing process including the deep drawing process is widely being used for the production of metallic cans for beverages such as beer, juice and gaseous drinks.
It is favorable to completely flatten the used cans for easier recycling procedure, but the cans made by the conventional one-sided ironing process cannot be well flattened manually by women and children but by a special machine.
In addition, the used cans are irregularly squashed by the conventional machine and are very often dangerous to injure the workers in their handling.
On the other hand, there is a different problem that the inner wall of such reinforcement members as shock absorber pipes has a rough surface and should be additionally polished to be of mirror surface.
The present invention has been developed considering the above-described problems in the extent of the conventional ironing technology. The objects of the invention is to provide a both-sided simultaneous ironing-deep drawing process, where vessels like metallic cans are strong enough during service but can easily be flattened by hand or foot squash after service.
Another object of the invention is to provide a both-sided simultaneous ironing-deep drawing process for producing such reinforcement members as shock absorber pipes which are longitudinally strengthened and have mirrored inner surface during the single stroke, while there is induced the residual compressive elastic stress in the circumferential direction.
For achievement of the above-described objects, the simultaneous both-sided ironing-deep drawing process of the present invention has been developed from such points of view as described below. The present inventors developed the both-sided ironing process by adding an inner die to the conventional outer die, and have so far been successful in achieving the mirror surface of inner wall during ironing and have found it possible to change the circumferential residual stress in the wall of the ironed cup (Refer to the Japanese Patent Publication Nos. 2088989, 2663150, and 2539618).
As regards the object of the present invention, it is necessary to investigate a relation between the longitudinal strength of the ironed cup and the relative geometry of outer and inner dies, to make possible the optimal selection of ironing process in relation with the required longitudinal strength of the ironed cup.
Further, the ironing condition is changed by vibrating either outer or inner dies during the ironing process to give additional changes in the residual stress and geometry of the ironed cup wall. Especially the geometrical change of the wall causes the unique point of wall strength to make easier the longitudinal squash of the cup.
In the simultaneous both-sided ironing-deep drawing process placing a work sheet (blank) and ironing the blank simultaneously with the outer and inner dies to prepare a tubular structure, the present invention relates to longitudinal wall strength change of the tubular structure by changing the height difference between the outer and inner dies as well as the die profile radii.
Thus, according to the present invention, for example, it is possible to control the longitudinal compressive resistance of the linear cup wall with the both-sided ironing process.
Furthermore, the present invention provides ring grooves in the wall of tubular structure by vibrating the outer and/or inner dies along the ironing direction, which causes the change of ironing rate and/or bending operation. The number of ring grooves depends on the frequency of vibration.
In other words, according to the present invention, the above-mentioned outer and inner dies are independent of each other, and both or either of them can be vibrated in the longitudinal or lateral direction to obtain the tubular structure with ring grooves.
The present invention can therefore provide the vessels of forcedly ring-grooved wall by vibrating the ironing die(s) in the direction perpendicular to the ironing direction.
The present invention relates to the serial installation of two or more outer and inner dies which can be independent of each other and can realize multi-stepped ironing process. Thus, the work of ironing can be divided to reduce the severity of ironing in each step and make higher the ironing limit.
Besides, according to the present invention, one or more of outer and/or inner dies which are installed in series can be vibrated in the ironing direction. The present invention makes possible to effectively produce the ring grooves in the wall of vessels by vibrating a part of multi-stepped dies.